Milk, metabolism and making it pay

Why do Scandinavian cows have good genes? How often do dairy cows have calves? Why are cows that produce more milk at greater risk of becoming infertile? I found answers to all these questions and more when I went to visit Professor Claire Wathes at the Royal Veterinary College.

It has been a summer of discontent in the dairy industry. Cuts to milk prices have hit the headlines and left many farmers fearing that they will no longer be able to make a profit from dairy farming. When profit margins are being squeezed, efficiency is paramount. Could research that sheds light on a costly area of wastage in the industry be used to inform and improve farming practice?

Claire Wathes is Professor of Veterinary Reproduction at the Royal Veterinary College. Her research, funded by the Wellcome Trust and others, focuses on ruminant reproduction, in particular the relationship between nutrition and reproduction in cattle and sheep. In a recent paper she has documented the mechanisms by which metabolic status – a measure of nutrient balance, body fat coverage, insulin-like growth factor levels and so on – affects fertility in the dairy cow.

Fertility is a critical factor in dairy farming. A high milk yield relies on a cow’s ability to calve and conceive again quickly and easily. Cows have a nine-month gestation period and produce milk for up to a year after calving, but the amount of milk produced dwindles over time. In order to produce as much milk as possible, a cow should calve every twelve months – which, if you do the maths, means that around two to three months after calving the cows are served (mated or, more often, artificially inseminated) and must conceive again. If they do not conceive within a reasonable time frame, they have to be culled.

The number of cows culled in the UK is a cause for concern within the industry. It is a welfare issue, but it is also a great waste of resources. An average Holstein dairy cow only recoups her rearing costs during her second lactation (Wathes 2012). Yet 15 to 20 per cent of dairy cows are culled in their first lactation, mainly due to poor fertility (Brickell & Wathes 2011).

Nutrition, fertility and genetics

Infertility problems in dairy cattle are multifactorial: genetics, age and health are just some of the factors that can influence an animal’s ability to conceive and remain pregnant. But Wathes’s extensive research in this area has shown that nutrient shortage is one common cause of reduced fertility.

“Cows have been genetically selected to produce a high milk yield. Large amounts of nutrients are targeted into milk production and, particularly in early lactation when milk production peaks, the cow will loose body weight and develop what we call a state of negative energy balance. This is when more nutrients are going into the milk than are being taken in in the diet. When this happens, the cow’s fertility becomes compromised.

“This problem can be eased with good management, but as milk yield goes up it becomes very much more difficult to ensure the cow has an adequate nutritional intake.”

Until recently, UK breeders selected animals almost exclusively on the basis of milk yield. Then, Wathes explains, people began to realise that they’d gone too far.

“Fertility was getting worse, disease incidence was getting worse: by focusing on milk alone farmers were ending up with animals that were more susceptible to all kinds of problems. So now when breeders select bulls to use for artificial insemination they take into account other factors as well, including measures of lameness, mastitis, and fertility in the daughters which the bulls produce.

“The Scandinavians, as it turns out, had always kept an eye on these other factors so some Scandinavian breeds have actually remained more fertile. Some UK farmers are now using those Scandinavian genetics to improve fertility in their cows.”

Poor nutrition can affect fertility indirectly by increasing a cow’s susceptibility to diseases such as mastitis or uterine infection.

“After calving, the uterus in the majority of cows develops a bacterial infection. If the cow is in good metabolic status she is normally able to clear that infection, but it seems that cows that are in a compromised nutritional status just don’t have the ability to mount an effective immune response, so the initial infection doesn’t clear up, it just rumbles on. The resulting inflammation can go on for months. When you then try to mate the cow, there is not a good uterine environment for the embryo.”

Knowledge is power

Wathes’s research also highlights the importance, and lasting impact, of the cow’s physical condition in the time leading up to calving.

“The immediate period around calving is absolutely crucial. There is a dip [in metabolic status] associated with calving. Healthier cows bounce back much more quickly. Cows that have a lower metabolic status before calving take longer to recover. When these cows are rebred after calving, those animals that have not recovered sufficiently will fail to conceive again.”

Information such as this could help farmers to improve the performance of their herd by investing wisely in both better nutritional management and improved genetic selection to improve fertility. But it’s vital that this information is communicated in the right way. Wathes is currently working with DairyCo, a levy-funded NGO for the UK dairy industry, to make sure that her work, and that of other researchers, is translated into useful advice for the farming community.

“We may be keen to improve the health and welfare of the cows, but there’s no point preaching high-minded ideas that are totally unrealistic. At the end of the day the farmer needs to make a profit. It’s got to work.”

References:

Brickell JS & Wathes DC (2011). A descriptive study of the survival of Holstein-Friesian heifers through to third calving on English dairy farms. Journal of dairy science, 94 (4), 1831-8 PMID: 21426972

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